Coating systems containing modified crosslinkers

ABSTRACT

The present invention provides a crosslinker for organic coatings having an amino resin core with substituents including more than one olefin functional group, a silicon-containing group, and at least one alkoxyalkyl or alkylol group. Coating compositions containing the crosslinker can be cured with radiation, especially ultraviolet radiation. The crosslinker can be included in a coating composition with one or more curable resins, applied onto a substrate and cured to form the cured coating of the invention.

This application is a divisional application of Ser. No. 09/747,716filed on Dec. 22, 2000, which is now abandoned.

FIELD OF THE INVENTION

This invention relates to coating systems with modified crosslinkers.More specifically, it relates to radiation and thermal curing of coatingsystems containing modified crosslinkers, and to the use of modifiedamino resins as crosslinkers for coating systems to improve scratch andmar resistance.

BACKGROUND OF THE INVENTION

Curable, or thermosettable, coating compositions are widely used in thecoatings art, particularly for topcoats in the automotive and industrialcoatings industry. Basecoat-clearcoat composite coatings are topcoatsthat offer exceptional gloss, depth of color, distinctness of image, orspecial metallic effects. The automotive industry has made extensive useof basecoat-clearcoat composite coatings for automotive body panels.Single layer topcoats and the clearcoats of color plus clear compositecoatings usually require an extremely high degree of clarity and glossto achieve the desired visual effect. Furthermore, they must maintainthe clarity and gloss over long periods of time in the face ofenvironmental challenges.

Clearcoat coating compositions used as the outermost automotive coatingare subject to damage caused by numerous elements. These elementsinclude environmental fall out, exposure to ultraviolet radiation fromsunlight, exposure to high relative humidity at high temperature, anddefects made by impacts of small, hard objects resulting in chipping.Topcoats and outer coatings in general can be formulated to reduce socalled scratch and mar, on the one hand, and environmental etch on theother. Scratch and mar refers to damage from impact, rubbing, orabrasion that produces visible scratches or marring that sometimes canbe rubbed out. “Environmental etch” is a term applied to a kind ofexposure degradation that is characterized by spots or marks on or inthe finish of the coating that often cannot be rubbed out.

In order to be commercially successful, a coating should provide as manyfavorable characteristics as possible. Accordingly, it is mostpreferable to produce a coating having an optimum mix of characteristicswith regard to various forms of damage resistance. For example, it wouldbe desirable to provide an increase in scratch and mar protectionwithout lessening the environmental etch protection.

A number of coating systems have been optimized over the years toprovide a favorable combination of these properties. However, becausethe systems represent a compromise, usually one property has been atleast partially sacrificed to increase the other. For example, a harderclearcoat film may be more resistant to environmental etch, but may bemore prone to damage by scratching. On the other hand, a softerclearcoat film may be more scratch resistant, but more susceptible toenvironmental etch.

In Gummerson, Journal of Coatings Technology, vol. 62, pages 43-49(1990), acrylated melamines in UV curable coatings are disclosed. Theacrylated melamines have both acrylic and alkoxy functionality. Themelamines may be UV cured by a free radical mechanism. However, themelamines have no silicon-containing groups. Furthermore, there is nodiscussion of improved scratch and mar resistance in cured filmscontaining the acrylated melamines.

In Strazik, U.S. Pat. No. 4,280,938, unsaturated condensates of analkoxy-methylmelamine, an allyl alcohol and an acrylamide are combinedwith an unsaturated oil modified resin in air drying compositions. Thecondensates contain olefin functionality and alkoxymethyl groups but donot have any silicon-containing groups. Furthermore, radiation curing isnot contemplated for the compositions containing the condensates.

In Deiner, U.S. Pat. No. 4,113,947, addition products are manufacturedfrom the reaction of nitrogen-containing compounds that contain at leastone ethylenically unsaturated radical (such as, for example,allylmelamine) with organopolysiloxanes which contain hydrogen atomsbonded to silicon. These addition products contain in their structure asilicon-containing group, but they have no remaining ethylenicunsaturation because the silicon-hydrogen bond of theorganopolysiloxanes reacts with the ethylenic unsaturation of thenitrogen containing compounds. As such, the addition products are notsuitable for use in radiation cured coatings.

An object of the invention is to provide compositions that can be addedin small amounts to coating systems to increase scratch and marresistance, while maintaining other desirable coating properties. Afurther object is to provide methods for making cured coatings havingimproved properties of scratch and mar resistance. Another object is toprovide a method for radiation curing for improving the scratch and marresistance of coatings.

These and other objects are achieved by the radiation and thermal curingof the compositions of the invention.

SUMMARY OF THE INVENTION

The invention provides a crosslinker for organic coatings having anamino resin core with substituents including an olefin functional group,a silicon-containing group, and at least one alkoxyalkyl or alkylolgroup. Coating compositions containing the crosslinker can be curedthermally and with radiation, especially ultraviolet radiation. Thecrosslinker can be included in a coating composition with one or morecurable resins, applied onto a substrate, and cured to form the curedcoating of the invention.

In a preferred embodiment, the crosslinker can be prepared by reactinga) alkoxyalkylated amino resin with b) an unsaturated compound having afunctional group reactive toward alkoxyalkyl groups and c) asilicon-containing compound having a functional group reactive towardalkoxyalkyl groups. In one embodiment, a coating composition containingthe crosslinker undergoes a stratification in the coating system towhich it is applied, so that the crosslinker is present at a relativelygreater concentration at the surface of the coating.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In one embodiment the invention provides a crosslinker with acombination of functional groups. The crosslinker has an amino resincore and, as substitutents on the amino resin core, at least one olefinfunctional group, a silicon-containing group, and at least onealkoxyalkyl or alkylol group. The functional groups on the amino resincore, as well as the relative proportions to one another, give thecrosslinker desirable properties.

At its core, the crosslinker has an amino resin structure. Amino resinsare the product of the reaction of various amines such as melamine,urea, guanidine, or benzoguanidine with an aldehyde such asformaldehyde, acetaldehyde, crotonaldehyde, benzaldehyde, and mixturesthereof. Examples of commonly used and well known amino resins includemelamine formaldehyde resins, urea formaldehyde resins, and guanidineformaldehyde resins. Amino resins are described in Encyclopedia ofPolymer Science and Technology vol. 1, p. 752-789 (1985), the disclosureof which is hereby incorporated by reference.

The reaction of the amine hydrogen and an aldehyde results in formationof an alkylol group on the nitrogen atoms of the amine. The structure ofthe alkylol group is derived from the alkyl chain of the aldehyde. Forexample, when the amine is reacted with formaldehyde, an amino resin isproduced with methylol groups on the nitrogen atoms.

The alkylol groups are capable of self reaction to form oligomeric andpolymeric materials. They are also reactive with a number of functionalgroups commonly found in conventional coating resins, such as hydroxylgroups, amino groups, and carbamate groups.

A preferred amino resin is one in which the alkylol groups have beenreacted with an alcohol to form so-called etherified amino resins.Commercially available amino resins include methylated, butylated, andisobutylated resins, which are produced by reaction of the alkylolgroups with methanol, butanol, and isobutanol respectively. Mixedetherified amino resins are prepared with combinations of two or moremono-functional alcohols. Mixtures of such resins are also useful.

The etherified amino resins are also known as alkoxyalkylated aminoresins, to emphasize that the amino resins contain alkoxyalkyl groups onthe nitrogens. Alkoxylated amino resins can be represented by theformula:

This represents in an idealized way the functional group resulting fromthe reaction of an amine R₁(NH₂)_(n) with an aldehyde R₂—CHO and analcohol R₃—OH, where R₂ is hydrogen or a C₁₋₂₀ alkyl or aryl group, R₃is C₁₋₂₀ alkyl or aryl group, R₁ represents the amino resin core whichcan be monomeric, oligomeric, or polymeric, and n is the number of aminegroups on the amino resin core. In the formula, X can be a hydrogen, analkylol group, or an alkoxyalkyl group. A commonly used aldehyde isformaldehyde, in which case R₂ is a hydrogen atom, and the functionalgroup on the nitrogen is an alkoxymethyl group.

The amino resins can self-condense to give oligomeric or polymericsubstances having a higher molecular weight. Monomeric materials and thelower molecular weight oligomers are commonly used in the coatingsindustry as crosslinking agents. Useful materials are characterized by adegree of polymerization. For melamine formaldehyde resins, it ispreferred to use resins having a number average molecular weight lessthan about 2000, more preferably less than 1500, and even morepreferably less than 1000.

The alkoxyalkyl and alkylol groups on the nitrogens of the amino resinsare reactive with a number of functional groups, which makes the aminoresins useful as crosslinkers for coating systems containing resinshaving those functional groups. As is known in the art, such functionalgroups include hydroxyl, amine, carbamate, thiol, and others.

A preferred amino resin is melamine formaldehyde resin. Such resins arereadily commercially available and have a desirably high functionality.The ideal monomeric melamine formaldehyde resin is hexafunctional, andall of the alkoxyalkyl, alkylol, or imino groups are available forreaction with functional groups such as those mentioned above.Commercially available melamine formaldehydes tend to have some two-ringand three-ring content, so that in practice the average functionalitywill be slightly higher than 6. The two ring compound, for example, isideally decafunctional. The functionality of the resin will be aweighted average of the functionalities of the one ring, two-ring,three-ring, etc. compounds present in the mixture. The functionality isalso related to the concept of equivalent weight. As used here, theequivalent weight is the molecular weight of the amino resin divided byits functionality as defined above.

The crosslinkers of the invention contain at least one, and preferablymore than one olefin functional group as constituents on the amino resincore. The olefin functional groups can be introduced by reacting theamino resin, preferably an alkoxyalkylated amino resin, and mostpreferably an alkoxymethylated amino resin, with an unsaturated compoundhaving a functional group reactive toward the amino resin or thealkoxyalkyl groups of the alkoxyalkylated amino resin. Examples of suchreactive functional groups include hydroxyl and amino groups, withhydroxyl being preferred.

Examples of unsaturated compounds include, without limitation,amino-functional olefins, hydroxyl-functional olefins, hydroxyalkylesters of unsaturated carboxylic acids, aminoalkyl esters of unsaturatedcarboxylic acids, and acrylamides.

Useful amino-functional olefins include, without limitation, C₃₋₂₀organic compounds having a carbon-carbon double bond and an amino group.Specific examples include allylamine, 4-amino-1-butene,6-amino-1-hexene, 8-amino-1-octene, 10-amino-1-decene,12-amino-1-dodecene, oleylamine, and the like.

Useful hydroxy functional olefins include organic compounds having acarbon-carbon double bond, a hydroxyl group, and 3-20 carbon atoms.Specific examples of hydroxyl functional unsaturated compounds include,without limitation, allyl alcohol; 1-buten-4-ol, 1-hexen-6-ol,1-octen-8-ol, 1-decen-10-ol, 1-dodecen-12-ol, oleyl alcohol, and thelike.

Hydroxyalkyl esters of unsaturated carboxylic acids may be prepared froma variety of unsaturated carboxylic acids, including alpha-betaunsaturated acids such as acrylic acid, methacrylic acid, and crotonicacid as well as other unsaturated carboxylic acids such as 3-butenoicacid, 4-pentenoic acid, and 5-hexenoic acid. Preferred hydroxyalkylesters are those with 2 to 10 carbon atoms in the alcohol portion.

Examples of hydroxyalkyl esters of unsaturated carboxylic acids include,without limitation, hydroxyethyl acrylate, hydroxyethyl methacrylate,hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutylacrylate, hydroxybutyl methacrylate, and mixtures thereof.

Preferred aminoalkyl esters of unsaturated carboxylic acids include,without limitation, those with 2-10 carbon atoms in the aminoalkylportion. The structures of the aminoalkyl esters are analogous to thestructures of the hydroxyalkyl esters described above. In the aminoalkylesters, the functional group reactive toward the amino resin will be anamino group. Preferred aminoalkyl esters of unsaturated carboxylic acidsinclude aminoethyl acrylate, aminoethyl metharylate, aminopropylacrylate, aminopropyl methacrylate, aminobutyl acrylate, aminobutylmethacrylate, and mixtures thereof.

Acrylamides are also useful as the unsaturated compound having afunctional group reactive toward the amino resin. Acrylamide andmethacrylamide are reactive toward the amino resin and are preferredacrylamide compounds. Other acrylamide derivatives include thoseanalogous in structure to the hydroxyalkyl esters and the aminoalkylesters of the unsaturated carboxylic acids, described above.

The unsaturated compound having a functional group reactive toward theamino resin reacts with alkoxyalkyl or alkylol groups on the amino resinto incorporate the olefin functionality of the unsaturated compound as asubstituent on the amino resin core.

The silicon-containing compound contains at least one silicon atom andfurther contains a functional group reactive toward the alkoxyalkyl oralkyol groups of the amino resin. Such a reactive functional group ispreferably a hydroxyl group or an amino group. A wide variety ofstructures is possible. For example, the silicon containing compound cancontain a single silicon atom to which an alkyl chain is attached, thealkyl chain being substituted with a functional group reactive toward analkoxyalkyl or alkylol group. Examples of such compounds include,without limitation, hydroxyalkyl trialkylsilanes such as hydroxymethyltrialkyl silanes or hydroxypropyl trialkyl silanes; and hydroxyalkylsilanes containing a mixture of alkyl and alkoxy groups on the siliconatom.

The silicon atom to which the alkyl chain is attached may alternativelybe part of a disiloxane or polysiloxane chain. A non-limiting examplewould be hydroxyalkyl substituted polydimethylsiloxanes.

The alkyl group attached to the silicon atom may also contain polyetheror polyester moieties terminated by a hydroxyl group or an amino group.Examples include ethoxylated, propoxylated, or butoxylatedhydroxyalkyl-substituted polydimethylsiloxanes, such as are commerciallyavailable from BYK Incorporated. In a preferred embodiment, thesilicon-containing compound comprises a polyester-modified polysiloxaneof general structure

where the R groups are independently C₁-C₂₀ alkyl or aryl groups,preferably methyl; R₁ is a C₁-C₂₀ bridging group, preferably methyleneor higher alkylene groups: y is 0 or greater; R₂ and R₃ are selectedfrom the group consisting of C₂-C₆ alkylene or benzene-diyl such asbenzene-1,2-diyl, benzene-1,3-diyl, and benzene-1,4-diyl; n is 1 orgreater, and n and y are chosen such that the hydroxyl number of theresulting polyester modified polydimethylsiloxane is from about 10 up toabout 200. Preferably, the hydroxyl number will be from about 15 toabout 180 mg KOH/g, and most preferably from 30 up to 160 mg KOH/g.Polyester-modified polysiloxanes are commercially available from BYKChemie.

A crosslinker of the invention preferably has more than one olefinfunctional group so that it crosslinks during radiation curing. It ismore preferred that the crosslinker have 2 or more olefin functionalgroups.

Crosslinkers with more than one olefin functional group can be preparedby reacting more than one equivalent of the unsaturated compound withthe amino resin or alkoxyalkylated amino resin. For example, where theamino resin is a hexafunctional melamine formaldehyde resin, enoughunsaturated compound should be reacted with the resin so as to add, onaverage, more than one olefin functional group per melamine ring. Thisis accomplished by using more than one equivalent of unsaturatedcompound for every 6 equivalents of the resin. Similarly, to producecrosslinkers preferably having two or more olefin functional groups, twoor more equivalents of the unsaturated compound should be reacted withthe amino resin. In the example of a melamine formaldehyde resin, two ormore equivalents of unsaturated compound may be used for every sixequivalents of resin.

A crosslinker of the invention preferably has at least onesilicon-containing group incorporated onto the amino resin core. Acrosslinker with at least one silicon-containing group on the core canbe prepared by reacting at least one equivalent of the siliconcontaining compound with the amino resin or alkoxy amino resin. Forexample, where the amino resin is a hexafunctional melamine formaldehyderesin, enough silicon-containing compound should be reacted with theresin so as to add on average at least one silicon containing group permelamine ring. This is accomplished by using at least one equivalent ofsilicon-containing compound for every six equivalents of the resin.Similarly, to produce crosslinkers having more than onesilicon-containing group per crosslinker molecule, more than oneequivalent of the silicon-containing compound should be reacted with theamino resin. In the example of a melamine formaldehyde resin, more thanone equivalent of silcon-containing compound may be used for every sixequivalents of resin.

In another embodiment, it may be useful to incorporate, on average, lessthan one silicon-containing group per crosslinker molecule. In such asituation, a crosslinker is produced where not all of the crosslinkermolecules have a silicon-containing group incorporated onto the resincore. Such crosslinkers may be incorporated into the coatingcompositions of the invention to provide increased scratch and marresistance. However, it will be appreciated that the effectiveness ofsuch crosslinkers for scratch and mar resistance may in general beproportionately lower than the crosslinkers containing amino resin coresthat are substituted with at least one silicon-containing group permolecule, on the basis of there being a lower concentration ofcrosslinker molecules containing the active silicon-containing group.

The reaction of the Unsaturated compound or silicon-containing compoundwith the amino resin can be conveniently carried out by refluxing thereactants together in a non-reactive solvent such as xylene or toluene.The reaction normally proceeds at a satisfactory rate without catalysis.If desired, catalysts can be added, such as toluene sulfonic acid orhydrochloric acid.

It is desirable to remove the alcohol formed during the reaction by, forexample, co-distilling or azeotroping it off along with the non-reactivesolvent. It may be desirable during the course of the reaction toreplace all or part of the non-reactive solvent distilled off. Theprogress of the reaction can be followed by determining, by gaschromatography or other known methods, the amount of alcohol or otherby-product produced. Normally for reaction with an alkoxyalkylated aminoresin, one equivalent of alcohol is liberated for every equivalent ofunsaturated compound or silicon-containing compound incorporated.

Subject to the discussion above, the crosslinker of the invention has atleast one alkoxyalkyl or alkylol group. In a preferred embodiment,alkoxalkyl groups are present in the amino resin starting material priorto reaction with the unsaturated compound or silicon containingcompound. In that case, some of the alkoxyalkyl groups of the aminoresin react with the unsaturated compound or the silicon containingcompound, as described above. It is important that not everyalkoxymethyl group on the amino resin core be reacted with the two abovecomponents, so that at least one alkoxyalkyl group is left on the aminoresin core.

In another embodiment, alkylol groups or a mixture of alkylol andalkoxyalkyl groups are present in the amino resin starting materialsprior to reaction with the unsaturated compound or thesilicon-containing compound. As above, at least one alkoxyalkyl oralkylol group should be left on the core after reaction with thecomponents. Any remaining alkylol groups on the crosslinker may beetherified, if desired, to form corresponding alkoxyalkyl groups.

The novel crosslinkers described above may be used in a coatingcomposition, optionally along with another conventional crosslinker thatdoes not have both the olefin functionality and the silicon containingfunctionality. The conventional crosslinker may or may not be an aminoresin, but it will contain functional groups reactive with the resins ofthe coating composition.

The crosslinker of the invention may be used in a minor amount relativeto the conventional crosslinker or to the crosslinking equivalents in aself-curing resin system. For example, it is preferred to use the novelcrosslinker in such an amount that from about 0.1 to about 20%, on anequivalent basis, of the resin-reactive functional groups of the totalcrosslinking composition are contributed by the crosslinker of theinvention. More preferably, from about 0.1 to about 10%, and mostpreferably from about 0.1 to about 3% on an equivalent basis of thefunctional groups in the crosslinking composition will be contributed bythe crosslinker of the invention.

As will be appreciated by one skilled in the art, the choice ofconventional crosslinking agent depends on various factors such ascompatibility with the film-forming resin, the particular type offunctional groups on the film-forming resin and the like. Thecrosslinking agent is used to crosslink the film-forming resin by eithercondensation reactions or non-free radical addition reactions or acombination of both of these. When for example the thermosettingreactants can be crosslinked in the presence of moisture or when thereactants include monomers having complementary groups capable ofentering into crosslinking reactions, the conventional crosslinkingagent may be omitted if desired.

Representative examples of conventional crosslinking agents includeaminoplasts, phenol/formaldehyde adducts, and crosslinkers havingblocked and/or unblocked isocyanate groups, epoxide groups, carbamategroups, siloxane groups, cyclic carbonate groups, or anhydride groups.Examples of such compounds include melamine formaldehyde resin(including monomeric or polymeric melamine resin and partially or fullyalkylated melamine resin), urea resins (e.g., methylol ureas such asurea formaldehyde resin, alkoxy ureas such as butylated ureaformaldehyde resin), polyanhydrides (e.g., polysuccinic anhydride), andpolysiloxanes (e.g., trimethoxy siloxane). Aminoplast resins such asmelamine formaldehyde resin or urea formaldehyde resin are especiallypreferred. When aminoplast resins are employed as the conventionalcrosslinking agent, particularly suitable are the melamine-formaldehydecondensates in which a substantial proportion of the methylol groupshave been etherified by reaction with a monohydric alcohol.

The coating compositions of the present invention contain thecrosslinking composition of the invention and a binder system containingat least one crosslinkable resin. Such crosslinkable resin or resins maycontain more than one kind of functional group, and may containfunctional groups reactive with each other. In the latter case the resinmay undergo crosslinking or curing with itself, perhaps even in theabsence of a separate crosslinking agent. When the resin or resinscontain only one kind of functional group, or when they have more thanone kind but the groups are not reactive with one another, aconventional crosslinker may be added to facilitate the curing process.At least one of the crosslinkable resins used has a functional groupwhich is reactive with the alkoxyalkyl or alkylol group or groups of thecrosslinker of the invention. With that limitation, a number ofcrosslinkable resins and conventional crosslinkers may be used in thecoating compositions of the invention.

As used herein, the term “crosslinkable resin” is intended to includenot only those resins capable of being crosslinked upon application ofheat but also those resins capable of being crosslinked without theapplication of heat. Examples of such crosslinkable resins includethermosetting acrylics, aminoplasts, polyurethanes, carbamate functionalresins, carbonate functional resins, polyesters, epoxies, silicones andpolyamides. These resins, when desired, may also contain functionalgroups characteristic of more than one class, as for example, polyesteramides, urethane acrylates, carbamate functional acrylates, etc.

Acrylic resins refer to the generally known addition polymers andcopolymers of acrylic and methacrylic acids and their ester derivatives,acrylamide and methacrylamide, and acrylonitrile and methacrylonitrile.Examples of ester derivatives of acrylic and methacrylic acids includealkyl acrylates and alkyl methacrylates such as ethyl, methyl, propyl,butyl, hexyl, ethylhexyl and lauryl acrylates and methacrylates, as wellas similar esters, having up to about 20 carbon atoms in the alkylgroup. Also, hydroxyalkyl esters can readily be employed. Examples ofsuch hydroxyalkyl esters include 2-hydroxyethyl acrylate,2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropylmethacrylate, 3-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate,and mixtures of such esters having up to about 5 carbon atoms in thealkyl group. Where desired, various other ethylenically unsaturatedmonomers can be utilized in the preparation of acrylic resins, examplesof which include: vinyl aromatic hydrocarbons optionally bearing halosubstituents such as styrene, alpha-methyl styrene, vinyl toluene,alpha-chlorostyrene; non-aromatic mono-olefinic and di-olefinichydrocarbons optionally bearing halo substituents, such as isobutylene,2,3-dimethyl-1-hexene, 1,3-butadiene, chlorethylene, chlorobutadine andthe like; and esters of organic and inorganic acids such as vinylacetate, vinyl propionate, isopropenyl acetate, vinyl chloride, allylchloride, vinyl alpha chloracetate, maleic acid and its monoesters,dimethyl maleate and the like.

The coating composition of the invention may contain as a crosslinkableresin an aminoplast resin different from the amino resin basedcrosslinker of the invention. As a crosslinkable resin, aminoplastresins refer to the generally known condensation products of an aldehydewith an amino- or amido-group containing substance examples of whichinclude the reaction products of formaldehyde, acetaldehyde,crotonaldehyde, benzaldehyde and mixtures thereof with urea, melamine orbenzoguanidine. Preferred aminoplast resins include the etherified (i.e.alkylated) products obtained from the reaction of alcohols andformaldehyde with urea, melamine, or benzoguanidine. Examples ofsuitable alcohols for preparation of these etherified products include:methanol, ethanol, propanol, butanol, isobutanol, t-butanol, hexanol,benzylalcohol, cyclohexanol, 3-chloropropanol, and ethoxyethanol.

Polyurethane or polyurea resins refer to the generally knownthermosetting resins prepared from organic polyisocyanates and organiccompounds containing active hydrogen atoms as found for example inhydroxyl, and amino moieties, respectively. Some examples ofpolyurethane resins typically utilized in coating compositions includethe isocyanate-modified alkyd resins. Examples of systems based onpolyurethane resins typically utilized as two-pack coating compositionsinclude an organic polyisocyanate or isocyanate-terminated prepolymer incombination with a substance containing active hydrogen as in hydroxylor amino groups together with a catalyst (e.g. organotin salt such asdibutyltin dilaurate). The active hydrogen-containing substance in thesecond pack typically is a polyester polyol, a polyether polyol, or anacrylic polyol known for use in such two-pack urethane resin systems.Another example of a polyurethane resin is a one pack system withblocked polyisocyanate and/or isocyanurates that unblock at hightemperatures. Hydroxyl terminated polyurethanes are also used as acrosslinkable resin.

Polyester resins are generally known and are prepared by conventionaltechniques utilizing polyhydric alcohols and polycarboxylic acids.Examples of suitable polyhydric alcohols include, without limitation,ethylene glycol, propylene glycol, diethylene glycol, dipropyleneglycol, butylene glycol, neopentyl glycol, glycerol, trimethylolpropane,pentaerythritol, sorbitol, 1,6-hexanediol, 1,4-cyclohexanediol,1,4-cyclohexanedimethanol, and 1,2-bis(hydroxyethyl)cyclohexane.Examples of suitable polycarboxylic acids include, without limitation,phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid,tetrahydrophthalic acid, hexahydrophthalic acid, tetrachlorophthalicacid, adipic acid, azelaic acid, sebacic acid, succinic acid, malicacid, glutaric acid, malonic acid, pimelic acid, succinic acid,2,2-dimethylsuccinic acid, 3,3-dimethylglutaric acid,2,2-dimethylglutaric acid, maleic acid, fumaric acid, and itaconic acid.Anhydrides of the above acids, where they exist, can also be employedand are encompassed by the term “polycarboxylic acid.” In additionlactones such as caprolactone, propylolactone, and methyl caprolactoneand hydroxy acids such as hydroxycaproic acid and dimethylolpropionicacid are useful. If a triol or higher hydric alcohol is used, amonocarboxylic acid such as acetic acid and benzoic acid may be used inthe preparation of the polyester resin. Moreover, polyesters areintended to include polyesters modified with fatty acids or glycerideoils of fatty acids (i.e. conventional alkyd resins). Alkyd resinstypically are produced by reacting the polyhydric alcohols,polycarboxylic acids, and fatty acids derived from drying, semi-drying,and non-drying oils in various proportions in the presence of a catalystsuch as sulfuric acid, or a sulfonic acid to effect esterification.Examples of suitable fatty acids include saturated and unsaturated acidssuch as stearic acid, oleic acid, ricinoleic acid, palmitic acid,linoleic acid, linolenic acid, licanic acid and elaeostearic acid.

Epoxy resins are generally known and are based on compounds or mixturesof compounds containing more than one 1,2-epoxy group (i.e.polyepoxides). The polyepoxides may be saturated or unsaturated,aliphatic, cycloaliphatic, aromatic or heterocyclic. Non-limitingexamples of suitable polyepoxides include the generally knownpolyglycidyl ethers of polyphenol and/or polyepoxides which are acrylicresins containing pendant and/or terminal 1,2-epoxy groups. Polyglycidylethers of polyphenols may be prepared, for example, by etherification ofa polyphenol with epichlorohydrin or dichlorohydrin in the presence ofan alkali. Examples of suitable polyphenols include without limitation1,1-bis(4-hydroxyphenyl)ethane; 2,2-bis(4-hydroxyphenyl)propane;1,1-bis(4-hydroxyphenyl)isobutane; 2,2-bis(4-hydroxylphenyl)ethane;2,2-bis(4-hydroxyphenyl)propane; 1,1-bis(4-hydroxyphenyl)isobutane;2,2-bis(4-hydroxytertiarybutylphenyl)propane;bis(2-hydroxynapthyl)methane; and the hydrogenated derivatives thereof.The polyglycidyl ethers of polyphenols of various molecular weights maybe produced, for example, by varying the mole ratio of epichlorohydrinto polyphenol. Epoxy resins also include the polyglycidyl ethers ofmononuclear polyhydric phenols such as the polyglycidyl ethers ofresorcinol, pyrogallol, hydroquinone, and pyrocatechol. Epoxy resinsalso include the polyglycidyl ethers of polyhydric alcohols such as thereaction products of epichlorhydrin or dichlorohydrin with aliphatic andcycloaliphatic compounds containing from two to four hydroxyl groupsincluding, for example, ethylene glycol, diethylene glycol, triethyleneglycol, dipropylene glycol, tripropylene glycol, propanediols,butanediols, pentanediols, glycerol, 1,2,6-hexanetriol, pentaerythritoland 2,2bis(4-hydroxycyclohexyl)propane. Epoxy resins additionallyinclude polyglycidyl esters of polycarboxylic acids such as thegenerally known polyglycidyl esters of adipic acid, phthalic acid, andthe like.

Addition polymerized resins containing epoxy groups may also beemployed. These polyepoxides may be produced by the additionpolymerization of epoxy functional monomers such as, without limitation,glycidyl acrylate, glycidyl methacrylate and allyl glycidyl etheroptionally in combination with ethylenically unsaturated monomers suchas styrene, alpha-methyl styrene, alpha-ethyl styrene, vinyl toluene,t-butyl styrene, acrylamide, methacrylamide, acrylonitrile,methacrylonitrile, ethacrylonitrile, ethyl methacrylate, methylmethacrylate, isopropyl methacrylate, isobutyl methacrylate andisobornyl methacrylate.

Carbamate-functional resins are known in the art to be useful inclearcoat compositions. One preferred carbamate-fuctional resin has aplurality of carbamate groups pendant to an acrylic backbone. Thecarbamate groups may be introduced into the resin by transcarbamation ofa hydroxyl functional resin following polymerization of acrylicmonomers, or may be prepared from acrylic monomers containing carbamatefunctional groups. Such carbamate functional acrylic resins aredescribed, for example, in Rehfuss et al., U.S. Pat. No. 5,605,965, thedisclosure of which is hereby expressly incorporated by reference.

Cured coatings are produced by applying onto a substrate a coatingcomposition of the invention. The coating composition includes one ormore of the crosslinkable resins having reactive functional groups andone or more crosslinking agents which have functional groups which arereactive with those of the resins, including at least one of thecrosslinkers of the invention. After application onto the substrate, thecoating composition is cured thermally and also by the application ofradiation, for example by electron beam radiation or ultravioletradiation. The thermal curing and the radiation curing steps may becarried out simultaneously. Alternatively, the thermal curing step mayoccur prior to the radiation curing step, or the radiation step may becarried out before the thermal curing step.

Thermal curing refers to the application of heat after the mixture hasbeen applied to substrate in order to accelerate the reactions betweenthe functional groups of the resin and the crosslinking agent or agents.For some crosslinkable systems, the curing temperature is well above thecoating temperature, so that essentially no thermal crosslinking takesplace until heat is applied. Other thermally curing systems are designedto cure, at least at a slow rate, even at room temperature. In thesesituations it can be said that the thermal curing begins immediatelyafter application of the coating composition onto the substrate. Ingeneral, it is preferred that the thermal curing step be carried out atleast in part before the radiation treatment is begun.

Radiation curing is carried out by exposing the curing composition toradiation, preferably in the form of electron beam radiation orultraviolet radiation. For ease of use and for cost considerations,ultraviolet radiation is preferred. When ultraviolet radiation is usedto cure the coating compositions, it is common to include in the coatingcompositions an activator which will promote the formation of radicalsfrom the double bonds present in the crosslinking composition. Dependingon the activators, the wavelength of ultraviolet radiation required canrange from 200 nanometers up to about 380 nanometers.

Without being bound by theory, it is believed that the crosslinker andthe coating compositions of the invention function in the following way.The silicon-containing crosslinker of the invention tends to migrate tothe surface of the coating composition. Thus the silicon containingcrosslinkers of the invention tend to be concentrated at the liquid toair interface of the coating composition which is at the surface so thatthe concentration of the crosslinker of the invention is greater in theliquid to air interface than in the bulk portion of the coatingcomposition. The olefin functionality on the novel crosslinker isavailable to participate in the radiation curing reaction byparticipating in 1,2 addition to itself under radical initiation. Thus,there is formed by radiation curing a crosslinked network ofsilicon-containing crosslinking agents with an enhanced concentration atthe surface of the coating. It is believed that this results in theincreased scratch and mar resistance of the resulting coatings. At thesame time, the alkoxyalkyl or alkylol groups of the crosslinker of theinvention react with the resins and anchor the crosslinking agent in thecoating. It is believed that this minimizes the problems of migrationthat otherwise tend to be observed with silicone additives and coatings.

The novel crosslinkers, coating compositions and methods for preparing acured coating have been described above with respect to preferredembodiments. The following examples give further non-limitingdescriptions of the use of the novel crosslinkers in the coatings of theinvention.

EXAMPLES

Resimine 737 is a methylated melamine formaldehyde resin, with anequivalent weight of about 130 per reactive functional group. Resimine747 is a hexamethoxymethyl melamine having an equivalent weight of about75 per methoxymethyl group. It is available commercially from Solutia.

BYK-LPG6962 is a hydroxy terminated polyester modified polydimethylsiloxane. It has a hydroxyl number of about 80 and an equivalent weightper hydroxyl of about 700. It is a commercial product of Byk Chemie.

MEK rubs is determined according to ASTM D-5402.

The mar rating is determined according to ASTM D-5178.

The Tukon hardness is determined according to ASTM D-1474.

The IR results are obtained by attenuated reflectance spectroscopy(ATR).

Preparation A

A round bottom flask was charged with 200 grams of Resimine 747 and 350grams of BYK-LPG 6962. The contents were heated with 250 grams oftoluene solvent to 130° C. and the methanol by-product was azeotropedoff. The extent of reaction was determined by measuring stoichiometricamounts of methanol given off by gas chromatography. When gaschromatography results indicated 90% theoretical completion of thereaction, 116 grams of hydroxyethyl acrylate was added along with 100grams of toluene and the azeotropic removal of methanol continued at130° C. until the reaction was judged to be over 90% complete based ongas chromatography results. The contents were cooled and the solidsadjusted to 60% by weight with toluene. The reaction product containstriazine ring and has about one silicon containing group, two acrylicgroups, and three methoxymethyl groups available for crosslinking with aprincipal resin.

Preparation B

A round bottom flask was charged with 200 grams of Resimine 747 and 180grams of BYK-LPG6962. The contents were heated with 250 grams of tolueneto 130° and the methanol by-product was azeotroped off. The extent ofthe reaction was followed by gas chromatography as in Preparation A.When the reaction was 90% complete, 116 grams of hydroxyethyl acrylatewas added along with 50 grams of toluene and the azeotropic removal ofmethanol continued at 130° C. until the reaction was 90% complete basedon gas chromatography. The contents were cooled and the solids adjustedto 60% by weight with toluene. The reaction product contains a triazinering with about two acrylic groups and three methoxymethyl groupsavailable for crosslinking with a principal resin. About half of thetriazine rings contain a silicon group.

Preparation C

In a reaction vessel, 420 g of hexamethoxymethylmelamine (HMMM, highmonomeric content, eq. wt 70 g/methoxymethyl group) with 292 g ofhydroxypropyl acrylate (HPA) and 200 g of xylene was heated to refluxunder a stream of air. Methanol by-product of the reaction was removedas an azeotrope with xylene. When the expected amount of methanol wascollected (about 64 g), 700 g of BYK-LPG6962 (silicon-containingcompound) was added and the azeotropic removal of methanol continued.When 32 g more of methanol was collected, enough xylene was added tomake the final concentration of product about 50% by weight. The IRspectrum of the crosslinker showed the presence of melamine triazinering, siloxane group, and double bonds. The GC also confirmed that theamount of unreacted HPA was less than 1%.

Preparation D—Basic Paint

A coating composition was prepared by combining an acrylic resin(equivalent weight of 425 grams per carbamate group) and Resimine 737(equivalent weight 130 grams per reactive functional group) inequivalent amounts. Two drops of dodecylbenzenesulfonic acid catalystwere added. Viscosity was adjusted with amyl acetate to a sprayviscosity of 30-40 seconds in a Ford #4 cup.

Examples 1-4

In Examples 1-4, fifty grams of preparation D was mixed with three gramsof the UV curable amino resin produced in Preparation B. In Examples1-3, the test formula also contained 0.3 grams of Genocure® MBFphotoinitiator.

Thermal curing was carried out at 260° F. for 30 minutes. Ultraviolet(UV) cure was performed with a hydrogen bulb at 95% intensity at 0.712J/cm². The conveyor speed was 16 feet per minute. Each panel wassubjected to two passes.

In Examples 1-4, the paints were spray coated onto a phosphatedelectrocoat primed steel panel. The mar test, double-rub test, Tukonhardness test, and attenuated reflectance IR test were performed on thecoated panels.

Comparative Example C1, prepared using Preparation C, did not containthe crosslinkers of the invention. The MEK rubs test is acceptable withgreater than 150 until failure. The mar rating of 2.5 and the Tukonhardness of 6.2 established a baseline against which the coatingcompositions of the invention were compared.

Examples 1 and 2 illustrate the effect of UV cure on coatingcompositions of the invention. In Example 1, the coating composition isthermally cured, but not UV cured. The mar rating is 3 and the Tukonhardness is 6.2. In Example 2, the coating composition of the inventionis both thermally cured and UV cured. The mar rating improvessignificantly to 2, and the Tukon hardness remains acceptable at 5.4.

Example 3 illustrates the importance of thermally curing the coatingcompositions of the invention. The MEK rubs were less than 20 and themar rating increased to 5. Example 4 illustrates the effect of curingcoating compositions containing the crosslinkers of the invention butnot containing ultraviolet photoinitiators. Without the photoinitiator,the UV cure did not improve the mar rating from the 2.5 of thecomparative example.

Infrared attenuated reluctance spectroscopy was used to determine thepresence of double bonds in the cured coatings of Examples 1-4. As notedin the footnotes of the Table, when the coating compositions of theinvention were thermally cured but not UV cured (Example 1), there wasinfrared evidence of double bonds at the surface of the composition.When the coating compositions underwent UV cure, the attenuatedreflectance spectroscopy indicated a lower amount of double bonds at thesurface than for the non-UV cured compositions. Example 3 illustratesthat even when the coating composition of the invention was notthermally cured, UV cure of the composition nevertheless resulted in areduced concentration of double bonds at the surface of the UV curecoating. Finally, Example 4 illustrates that when thermal cure andultraviolet cure are both carried out, but the ultraviolet cure iscarried out in the absence of a photoinitiator, the results resemblethose of Example 1 where the ultraviolet cure was not carried out.

Examples

C1 1 2 3 4* Preparation C 50 50 50 50 50 Preparation B − 3 3 3 3 Thermalcure + + + − + uv cure − − + + + MEK rubs >150 >150 >150 <20 >150 Marrating 2.5 3 2 5 2.5-3 Tukon hardness 6.2 6.2 5.4 − 6.7 IR − (1) (2) (3)(4) (1) evidence of double bonds on the surface (2) fewer double bondson the surface than in Example 1 (3) like Example 2 (4) like Example 1*contains no photoinitiator

Example 5

243 g of acrylic clearcoat resin (containing hydroxyl groups) was mixedwith 6 grams of the silicon-containing experimental melamine crosslinkerof Preparation C. The mixture was spray coated with a mixture ofisophorone isocyanurates and hexamethylene isocyanurates (64 g)—2 feedsystem on to a black waterborne basecoat on a primered steel panel tomake a test panel. A control panel was produced by spraying theclearcoat resin without the experimental crosslinker. The coated panelswere cured at 250° F. for 30 minutes. One half of each panel was coveredwith aluminum foil and the panels were subjected to UV cure with ahydrogen bulb at 95% intensity at 0.712 J/cm², with two passes. Theconveyor speed was 16 feet per minute. Thus both halves of the panelswere thermally cured, but only one half was UV cured.

The cured panels were tested by ATR. Both the covered (non-UV cured) andthe uncovered (UV-cured) halves of the test panel coated with acomposition containing the experimental crosslinker showed the presenceof melamine and siloxane peaks at the surface. The covered half had moredouble bond character than the uncovered half.

The panels were subjected to the ASTM scratch and mar test, along withmeasurements of gloss before and after the test. The covered half of thetest panel (the half not UV cured) retained only 79% of the initialgloss after the scratch and mar test. On the other hand, the UV curedhalf retained 86% of gloss. With the control panel, the exposed andcovered portions did not show any difference in gloss retention.

The invention has been described in detail with reference to preferredembodiments thereof.

We claim:
 1. A composition comprising a crosslinker for organic coatingscomprising the reaction product of a) an amino resin comprising reactivegroups selected from the group consisting of alkoxyalkyl, alkylol, andmixtures thereof; b) an olefinically unsaturated compound having afunctional group reactive toward the reactive groups on the amino resin,wherein the olefinically unsaturated compound is selected from the groupconsisting of amino-functional olefins, hydroxyl functional olefins,aminoalkyl esters of unsaturated carboxylic acids and acrylamides; andc) a silicon-containing compound having a functional group reactivetoward the reactive groups on the amino resin.
 2. The compositionaccording to claim 1, wherein the amino resin comprises a melamineformaldehyde resin.
 3. The composition according to claim 2, wherein themelamine formaldehyde resin has a number average molecular weight of upto about
 2000. 4. The composition according to claim 1, wherein thesilicon-containing compound comprises a silicon atom to which an alkylchain is attached, said alkyl chain being substituted with a functionalgroup reactive toward the reactive groups on the amino resin.
 5. Thecomposition according to claim 1, wherein the silicon-containingcompound comprises a compound of structure:

where the R groups are each independently C₁-C₂₀ alkyl or aryl groups;R₁ is a C₁-C₂₀ bridging group; y is 0 or greater; R₂ and R₃ are eachindependently selected from the group consisting of C₂-C₆ alkylene,benzene-1,2-diyl, benzene-1,3,-diyl, and benzene-1,4-diyl; n is 1 orgreater, and the hydroxyl number is from about 10 mg KOH/g up to about200 mg KOH/g.
 6. The composition according to claim 1, wherein thecrosslinker comprising 2 or more olefin functional groups.